When BM from mice pre-treated with 5-fluoro uracil (5-FU), which enriches multi-potential myeloid cells in the BM, were transplanted to recipient mice all three isoforms of BCR-ABL gave rise to CML like disease in all mice with similar latency for development of disease. This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.